The present invention is related to an improvement in ceramic slip and tape casting compositions. In particular, the present invention is directed to ceramic casting compositions which utilize organic solvents. More particularly, the present invention is directed to the use of a particular class of dispersing agents for the inorganic casting compositions.
The following factors must be examined to determine if a good casting composition has been formed: viscosity; settling rate; sensitivity to mold conditions; release properties; shrinkage during drying; drain properties; strength of cast wear; casting rate; freedom from foaming; and finally, low evaporation rate of vehicle. The characteristics of a good casting composition are: (1) the slip must pour easily and fill all the details of the mold and should not exhibit significant yield point or pronounced dilatency or thixotropy; (2) the particles in the casting composition should not settle too quickly to the bottom otherwise the casting composition or casted product will have tapered walls and thick bottoms and the final fired ceramic part will have an excessive number of flaws or defects; (3) the casting composition must release from the mold fairly easy and should not shrink to excessive amounts during drying; (4) the strength of the cast object prior to firing must be sufficient to allow handling, trimming or further shaping of the cast article; (5) the rate of casting when utilizing the composition should be such as to be consistent with reasonable production rates and good properties; (6) the casting composition should not produce an excessive amount of foam which would result in the entrapment of air bubbles in the prefired cast object; and (7) the solvent used for the casting composition should have a relatively low evaporation rate so that a dry film does not form on the exposed surface of the cast composition.
Typically, prior casting compositions containing organic solvents have used polymers and copolymers of natural or synthetic materials as the dispersing agents Examples of these types of materials include fish oil, a cross-linked fatty acid triglyceride, corn oil, an unsaturated fatty acid glyceride and LB 2155 (a polyisobutenyl succinimide) produced by Lubrizol Corp.. While all these materials produce adequate organic casting compositions, there is substantial room for improvement. It is the object of the present invention to provide improved casting or slip composition utilizing a unique dispersing agent.